/**
 * Abstract base class of interpolants over parametric samples.
 *
 * The parameter domain is one dimensional, typically the time or a path
 * along a curve defined by the data.
 *
 * The sample values can have any dimensionality and derived classes may
 * apply special interpretations to the data.
 *
 * This class provides the interval seek in a Template Method, deferring
 * the actual interpolation to derived classes.
 *
 * Time complexity is O(1) for linear access crossing at most two points
 * and O(log N) for random access, where N is the number of positions.
 *
 * References:
 *
 * 		http://www.oodesign.com/template-method-pattern.html
 *
 */

class Interpolant {
  constructor(parameterPositions, sampleValues, sampleSize, resultBuffer) {
    this.parameterPositions = parameterPositions;
    this._cachedIndex = 0;

    this.resultBuffer = resultBuffer !== undefined ? resultBuffer : new sampleValues.constructor(sampleSize);
    this.sampleValues = sampleValues;
    this.valueSize = sampleSize;

    this.settings = null;
    this.DefaultSettings_ = {};
  }

  evaluate(t) {
    const pp = this.parameterPositions;
    let i1 = this._cachedIndex;
    let t1 = pp[i1];
    let t0 = pp[i1 - 1];

    validate_interval: {
      seek: {
        let right;

        linear_scan: {
          // - See http://jsperf.com/comparison-to-undefined/3
          // - slower code:
          //-
          // - 				if ( t >= t1 || t1 === undefined ) {
          forward_scan: if (!(t < t1)) {
            for (let giveUpAt = i1 + 2; ; ) {
              if (t1 === undefined) {
                if (t < t0) break forward_scan;

                // after end

                i1 = pp.length;
                this._cachedIndex = i1;
                return this.afterEnd_(i1 - 1, t, t0);
              }

              if (i1 === giveUpAt) break; // this loop

              t0 = t1;
              t1 = pp[++i1];

              if (t < t1) {
                // we have arrived at the sought interval
                break seek;
              }
            }

            // prepare binary search on the right side of the index
            right = pp.length;
            break linear_scan;
          }

          // - slower code:
          // -					if ( t < t0 || t0 === undefined ) {
          if (!(t >= t0)) {
            // looping?

            const t1global = pp[1];

            if (t < t1global) {
              i1 = 2; // + 1, using the scan for the details
              t0 = t1global;
            }

            // linear reverse scan

            for (let giveUpAt = i1 - 2; ; ) {
              if (t0 === undefined) {
                // before start

                this._cachedIndex = 0;
                return this.beforeStart_(0, t, t1);
              }

              if (i1 === giveUpAt) break; // this loop

              t1 = t0;
              t0 = pp[--i1 - 1];

              if (t >= t0) {
                // we have arrived at the sought interval
                break seek;
              }
            }

            // prepare binary search on the left side of the index
            right = i1;
            i1 = 0;
            break linear_scan;
          }

          // the interval is valid

          break validate_interval;
        } // linear scan

        // binary search

        while (i1 < right) {
          const mid = (i1 + right) >>> 1;

          if (t < pp[mid]) {
            right = mid;
          } else {
            i1 = mid + 1;
          }
        }

        t1 = pp[i1];
        t0 = pp[i1 - 1];

        // check boundary cases, again

        if (t0 === undefined) {
          this._cachedIndex = 0;
          return this.beforeStart_(0, t, t1);
        }

        if (t1 === undefined) {
          i1 = pp.length;
          this._cachedIndex = i1;
          return this.afterEnd_(i1 - 1, t0, t);
        }
      } // seek

      this._cachedIndex = i1;

      this.intervalChanged_(i1, t0, t1);
    } // validate_interval

    return this.interpolate_(i1, t0, t, t1);
  }

  getSettings_() {
    return this.settings || this.DefaultSettings_;
  }

  copySampleValue_(index) {
    // copies a sample value to the result buffer

    const result = this.resultBuffer;
    const values = this.sampleValues;
    const stride = this.valueSize;
    const offset = index * stride;

    for (let i = 0; i !== stride; ++i) {
      result[i] = values[offset + i];
    }

    return result;
  }

  // Template methods for derived classes:

  interpolate_(/* i1, t0, t, t1 */) {
    throw new Error('call to abstract method');
    // implementations shall return this.resultBuffer
  }

  intervalChanged_(/* i1, t0, t1 */) {
    // empty
  }
}

// ALIAS DEFINITIONS

Interpolant.prototype.beforeStart_ = Interpolant.prototype.copySampleValue_;
Interpolant.prototype.afterEnd_ = Interpolant.prototype.copySampleValue_;

export { Interpolant };
